The function ch_ns_point finds the points of a given set of input points with minimal and maximal $$x coordinates.
#include <CGAL/ch_selected_extreme_points_2.h>
 

 
traverses the range [first,beyond). After execution, the value of n is an iterator in the range such that *n $$ _{yx} *it for all iterators it in the range. Similarly, for s the inequality *s $$ _{yx} *it holds for all iterators in the range. 
The default traits class Default_traits is the kernel in which the type ForwardIterator::value_type is defined.
CGAL::ch_e_point
CGAL::ch_nswe_point
CGAL::ch_n_point
CGAL::ch_s_point
CGAL::ch_w_point
CGAL::ch_we_point